Power transmitting apparatus



July 10, 1945. D. E. JEWITT POWER TRANSMITTING APPARATUS Filed Aug. 11, 1942 His Attorney- Patented July 10, 1945 2,389,243 rowan TRANSMITTING IAPPARATUS Dennis Ernest Jewitt, Rugby, England. assignor to General Electric Company, a corporation of New York Application August 11, 1942, Serial No. 454,401.

. In Great Britain August 18, 1941 4 Claims.

This invention relates to power transmitting apparatus for transmitting power from two or more prime movers to a single shaft or to two or more shafts. and more particularly to such apparatus adapted for ship propulsion purposes where the prime movers employed are such as to develop their designed maximum output at a predetermined speed.

It is well known that in such systems the emcient use of the power available can only be made when the prime movers employed are all operating at the speed at which they develop their maximum power output. If all the prime movers are maintained in operation at a reduced speed, a considerable lowering of efiiciency results and an uneconomical running is obtained.

It is an object of the invention to provide an efficient and economical power transmitting system capable of operating at different speeds and employing a plurality of prime movers of such a nature that they operate with greatest efficiency at or about a given speed.

It is a further object of the invention to provide a ship propulsion system using a plurality of prime movers of the character above set forth in which to obtain reduced speed with maximum efli'ciency only certain of the prime movers are utilised to obtain a lower propulsion speed.

It is another object of the invention to provide a ship propulsion system in which electrodynamic power transmitting couplings are employed between the prime movers and the propeller shaft or shafts, the slip energy developed in one of said couplings, when the prime movers associated therewith remains in operation at its maximum speed, being supplied to the remaining couplings, the prime movers associated therewith being locked against rotation, 50 that the propeller shafts driven thereby operate at substantially the same speed as the shaft associated with the prime mover which remains in operation.

Other objects and advantages of the invention will appear as the specification proceeds.

It has been suggested in the specification of United States Letters Patent No.'1,047,858 assigned to the assignee of the present application, to utilise for driving a pair of propeller shafts in a ship propulsion scheme, two steam turbines which drive the shafts through a species of elecpossible to supply the slip energy developed in one of the electric clutches associated with the turbine remaining in operation to the electric clutch associated with the fixed turbine to drive both propeller shafts from one turbine. The arrangement described however, did not enable the turbine remaining in operation to develop its maximum load as it would be inferred that the couplings were provided with equal numbers of poles, and the power output of the turbine remaining in operation was reduced approximately to one-quarter of its designed full-load output.

In carrying out the present invention I provide an arrangement which, while in many respects similar to that disclosed in the specification above referred to, differs therefrom in that the number of poles provided on the electro-dynamic power transmitting couplings is chosen to have a predetermined relationship, such that when one of the prime movers is stopped and the prime mover remaining in operation is rotating at its maximum speed and developing its maximum power output, the slip energy from its coupling is supplied to the other coupling which then functions as a motor, enables the speeds of the shafts driven through the electric couplings to be substantially equal. A considerable increase in the utilisation of the power available is thereby obtained as will be appreciated by those skilled in the art.

The invention will best be understood from reference to the following description taken in connection with the accompanying drawing which shows in Figs. 1 and 1a the lay-out and electrical connections respectively of one arrange-' ment embodying the invention; while Figs. 2 and 2a are similar diagrams of an alternative and preferred embodiment of the invention.

Referring now to Figs. 1 and 1a of the drawing, I have shown at i and 2 two prime movers, which may be internal combustion engines, driving through electro-dynamic power transmitting couplings 3 and 4 respectively, and through a speed mechanical coupling consisting of a speed reducing gear box 5 on to a propeller shaft 6. The couplings 3 and 4 each comprise a field-producing structure and an armature associated therewith, and may be constructed in all essential details as polyphase A. C. generators except that both the field-producing structures and armatures are mounted for rotation. Both couplings may also be provided with pole face squirrel cage windings. The field-producing structures may be connected to the associated prime mover and the armature to the gear box, or vice versa. In Fig. 1a the fieldproducing structures are indicated at 'i and 8 respectively, while the armatures are indicated at 3 and Ill. The fields are shown as being supplied from a source of excitation ll through switches I2 and I3. Electrical connections 14 are provided between the armatures through change over switches l and 46 respectively, which are arranged when closed in the upper position to short-circuit the armatures and in the lower position to interconnect the armatures with one an other.

It is well known that internal combustion engines develop their maximum power with greatest efficiency at a given speed, the power capacity diminishing with diminution of speed. If, therefore,'it is desired to reduce the speed of the pro-. peller shaft and the speed of the two prime movers l and 2 are both reduced, a considerable reduction in efficiency will result. In normal conditions, with prime movers I and 2 in operation, the

switches l5 and It will be closed in their upper positions to short circuit the armatures of the couplings 3 and 4, and the couplings will transmit the power developed by the two prime movers through the mechanical power transmitting couplings or gear box 5 to the shaft 6, the slip between the field-producing structures and the armatures of the couplings 3 and 4 being just suflicient to maintain circulation of the requisite current in the armatures.

Now according to the invention we provide one i of the prime movers, say 2, with means for holding it stationary, and arrange that the number of poles provided on the field-producing structure of the coupling 3 is higher than and bears a predetermined relationship to the number of poles provided on the coupling 4. 11', now, prime mover I'continues to rotate at a speed such as to develop its maximum power, greater slip energy will be induced in the armature 9 thereof. This slip energy is supplied to the armature ID, by closing is approximatel 80% of the speed with full power input. To find a suitable number of poles for the two couplings 3 and 4, let X=pole number on the driven engine coupling, and Y=pole number on the stationary engine coupling. Now, 20X=80Y,

and

Coupling 3 may therefore be provided with say, 32' poles and coupling 4 with 8 poles. The shafts leading from the couplings 3 and 4 to the mechanical coupling 5 will then rotate at equal speeds with the prime mover I developing v its maximum power out-put and the shaft 6 rotating at approximately 80% of normal speed.

Prior to the stopping of one prime mover and the utilisation of the slip energy in one coupling by a change-over of switches l5, IS, the propeller speed may be reduced to about 71% of normal by the reduction in the speed of the prime movers, when 50% of full power torque will suffice to drive the propeller and one prime mover can be disconnected. After the shaft of the prime mover 2 has been locked to a standstill and the switches II, It have been closed on to the bottom contacts,

prime mover number I may be run at about of its normal speed. On closing switch l2, coupling 3 exerts a turning effect and the slip energy transferred through switches It, It causes coupling 4 to function as a squirrel cage motor. When acceleration is completed, switch l3 may be .closed to excite the field-producing structure of coupling 4, and prime mover I run up to its maximum speed.

In addition to their function as a means for transferring and utilising slip energy, the couplings 3 and 4 will also function, where the prime movers l, 2, develop an irregular torque, e. g. in the case of heavy oil engines, as shock absorbing couplings between the prime mover and the mechanical power transmitting coupling 5.

It will be evident that in place of utilising the mechanical coupling 5, the prime movers may each drive through the couplings 3, 4 separate propeller shafts, as in the case of a twin-screw ship, and the two propeller shafts may be driven with one only of the prime movers in operation. Since, however, the speed-reducing mechanical coupling 5 is commonly necessary, an arrangement embodying the same has, been referred to.

The invention may be employed with even greater advantage in the case of a triple-screw propulsion system, an example of which is shown in Figs. 2 and 2a of the drawing. In this arrangement three pairs ofprime movers, electrodynamic and mechanical couplings are employed in place of the single pair shown in Fig. 1. Parts corresponding to similar parts in Fig. l have been assigned the same reference numerals with the addition of one prime for one additional (lefthand) set and two primes for the second additional (right-hand) set. The armatures of couplings 3, 4' are adapted for interconnection with the armature of coupling 3 and the armatures of coupling 3", 4" are adapted for interconnection with the coupling 4. With the arrangement shown in Figs. 2 and 2a, it is intended that when one-third power is to be developed prime movers I and 2 will be maintained in operation at their maximum power out-put, the slip energy in couplings 3 and 4 bein supplied to the couplings 3, 4 and 3", 4" respectively. Again assuming that the power necessary varies as the cube of the speed, at one-third power the appropriate speed will be 69.1% of full power speed. The numbers of poles provided on couplings 3 and 4 will then be greater than the number of poles provided on couplings 3', 4' and 3", 4", in the proportion A suitable combination of pole numbers will then be poles on couplings 3', 4 and 3", 4" and 112 poles on couplings 3, 4.

In some cases it is considered more eiiicient from a ship propulsion aspect when cruising to develop appreciably more power on the centre screw than on the wing screws. With .the arrangement above described, the distribution of power between the three shafts assuming equal shaft speed would be 69.1% on the centre shaft, and 15.4% on each of the wing shafts.

As an alternativefthe couplings 3', 4' and 3", 4" may be provided with the higher number of poles and the couplings 3, 4 with the lower num ber. In this event, I have .the possibility of selecting any two prime movers I, 2, or I", 2" as the prime mover to be utilised when the lower power output is required, the interconnections between the armatures being suitably arranged to utilise the slip energy developed.

The difierence in pole numbers employed on the different electro-dynamic couplings when functioning as slip couplings has no effect on the efiiciency of the circuit.

It is obvious that starting and speed control devices such as are commonly employed with induction motors may be incorporated in the present; system for starting and maneuvering. It is also obvious that one or more of the prime movers may be reversed for purposes of reversing and maneuvering the ship; for example, if the prime mover I in Fig. 1 is reversed, then the ship may be driven either ahead of astern depending on whether the coupling 4 or .the coupling 3 is excited.

While I have shown particular embodiments oi. my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a power transmitting system a plurality oi prime movers, a plurality of shafts each driven by one of said prime movers, electro-dynamic power transmitting couplings interposed in the connections between each of said prime movers and the shaft driven thereby, said couplings each consisting of a field-producing structure and an armature associated therewith, one of which is connected to the prime mover and the other to the shaft, the number of poles provided on said field-producing structure associated with at least one of said prime movers being higher than and bearing a predetermined relation to the number provided on said structures associated with the remainder of said prime movers, means for holding stationary said remainder of prime movers and means for supplying to the armatures or the couplings associated with said remainder 01' prime movers the slip energy developed in the armature associated with said one 01 said prime movers when said one prime mover continues to rotate, while said remainder of prime movers is held stationary, whereby by reason of the said predetermined relation of the pole numbers to produce substantially equal speeds oi. rotation of all of.

said shafts while maintaining full load on said one prime mover.

2. In combination a pair of prime movers a driven shaft, 9. common mechanical coupling between said prime movers and said shaft, an electro-dynamic power-transmitting coupling interposed in the connection between each prime mover and said common mechanical coupling, said electro-dynamio couplings each consisting of a field-producing structure and an armature associated therewith, one of which is connected to the appropriate prime mover and the other to said common mechanical coupling, the number of poles provided on one 01' said field-producing structures associated with one prime mover being higher than and having predetermined relation to the number oi poles provided on the field producing structure associated with the other prime mover, means for holding stationary said other prime mover, and means for supplying to the armature 01' the coupling associated with said other prime mover the slip energy developed in the armature of said electro-dynamic coupling associated with said one prime mover when said one prime mover continues to. rotate while said other prime mover is held stationary whereby the predetermined relation between said pole numbers is such as to tend to produce substantially equal speeds of rotation of the elements of said electro-dynamic couplings associated with the common mechanical coupling while the prime mover which continues to rotate is developing its maximum power.

3. In an electric ship propulsion system, three prime movers each adapted to operate eiiiciently at a given speed, three propeller shafts each driven by one of said prime movers, electro-dynamic couplings interposed between each of said prime movers and the shafts driven thereby, said couplings each consisting of a field-producing structure and an armature associated therewith, one of which is connected to the prime mover and the other to the shaft, the number of poles provided on one of said field-producing-structures being higher than that provided on the remaining two of said structures, means for holding stationary the prime movers associated with the couplings having the lower number of poles on their field-producing structures, and means for supplying to the armatures of the couplings having the lower number of poles the slip energy developed in the armature of remaining coupling when the prime mover associated therewith continues to rotate at its given speed while the other prime mover is held stationary whereby by reason of the predetermined relation of the pole numbers to produce substantially equal speeds of rotation of all of said shafts while maintaining full load on said one prime mover.

4. In an electric ship propulsion system three pairs of prime movers each adapted to operate efficiently at a given speed, three propeller shafts each adapted to be driven by one of said pairs of prime movers, a mechanical speed reduction coupling connecting each of said pairs of prime movers to the appropriate one of said shafts, electrodynamic couplings interposed between each of said prime movers and said mechanical coupling connected thereto, said electro-dynamic couplings each consisting of a field-producing structure and an armature associated therewith, one of which is connected to the prime mover and the other to one of said mechanical couplings the number of poles provided on the field-producing structures associated with one of said pairs of prime movers being higher than that provided on the structures associated with the other two or said pairs of prime movers, means for holding stationary said other two pairs of prime movers. and means for supplying to the armatures of the couplings having the lower number of poles the slip energy developed in the amature of the remaining coupling having the higher number of poles when the pair of prime movers associated therewith continues to rotate at their given speed while the other pairs of prime movers are held stationary whereby by reason of the predetermined relation of the pole numbers to produce substantially equal speeds of rotation of all or said shafts while maintaining full load on said one pair of prime movers.

DENNIS ERNEST JEWITT. 

